The present invention relates to a process for producing pitch carbon fibers which are of excellent interfiber separability.
Pitch carbon fibers are produced by subjecting pitch fibers obtained by the melt spinning of a carbonaceous pitch to infusiblization and carbonization, and, additionally as needed, graphitization. The infusiblization treatment of pitch fibers, which is carried out usually at a temperature of 400.degree. C. or below in the presence of an oxidative gas, is encountered with a problem for the pitch fibers to be adhered to each other during the infusiblization reaction. Moreover, in the subsequent carbonization step there also arises mutual adherence between the fibers though being to a slight extent. In either case, carbon fibers of good interfiber separability cannot be obtained from such mutually adhered fibers.
Heretofore, there is known an infusiblization treatment of pitch fibers following application of an oily agent, for example, technique to form pitch fiber tows by means of a water-soluble surface-active agent (Japanese Patent Publication No. 12740/1976). However, use of a water-soluble surface-active agent did reduce the interfiber separability in the infusibility treatment of fiber tows due to interaction between the surface-active agent and the fibers at higher temperatures although it improved tow formation of the fibers.